Background for this one: for a couple of years there was a dedicated non-stop shuttle bus (route T123) between Feltham station and Heathrow Central Bus Station for which you could get a through rail ticket from any NR station printed to the destination HEATHROW/FLTMBUS. (Now, TfL route 285 accepts through tickets, but they are only available from a limited range of stations and are just issued to Heathrow Airport).
Anyway, to get this ticket into my collection, I somehow persuaded my parents to take this route when we flew from Heathrow to Belfast in 1999. Our journey was Hassocks > Clapham Junction > Feltham, and we needed to connect between Pfms 12 and 6. The train was several minutes late by the time we arrived at CJ, but with luggage, two 50-something parents and the hideous subway to negotiate, we managed the 30-second connection to the fast train to Feltham. Admittedly a bit pointless, because the service is quite frequent to Feltham!